Primarily during heart operations there is a transient need to replace the function of the heart and lungs by artificial means. Also in more chronic disease states as e.g. during severe pulmonary, cardiac, or renal failure, maintenance of life can be upheld by different artificial means until an organ for transplantation becomes available. In many clinical situations there is a need for an extracorporeal circuit wherein the artificial organ is incorporated.
The contact of blood on surfaces made out of foreign material inevitably initiates blood coagulation and the formation of clots. This is controlled by the use of anticoagulant drugs. Also gas bubbles are easily formed in blood, which is propelled into the circulation of a living being during extracorporeal circulation. This phenomenon is due to cavitation, temperature gradients, and differences in the amount of gases dissolved between own and incoming blood. In the case of heart surgery the extracorporeal circuit contains a gas-exchange device i.e. an oxygenator, which is used not only for oxygenation but also for the disposal of carbon dioxide. The close contact between blood and gas in the oxygenator poses even higher risks for inadvertent entry of gas bubbles into the circulating blood.
At present, to avoid bubble formation during heart surgery membrane-type oxygenators are used instead of bubble-oxygenators, high temperature gradients are avoided, and use of suction in the operating field is controlled. Heart-lung machines contain an air bubble sensor that warns the perfusionist, i.e. the person maneuvering the heart-lung machine, of the appearance of small bubbles and immediately stops the main pump when larger bubbles appear. Typically, the bubble sensor can discern bubbles with a diameter of approximately 0.3 mm, and stops the main pump when a bubble with a diameter of 3-5 mm is recognized.
Cardiac surgery is frequently complicated by postoperative neurocognitive deficits that degrade functional capacity and quality of life while increasing healthcare costs. Multifactorial contributors to this significant public health problem likely include gaseous microemboli (GME). The arterial circulation receives thousands of 10-40 μm GME during cardiopulmonary bypass (CPB) despite the use of membrane oxygenation and arterial filtration. Vasooclusive GME cause tissue ischemia and denude endothelium in the brain and other end organs, leading to vascular dilation, increased permeability, activation of platelets and clotting cascades, and recruitment of complement and cellular mediators of inflammation.
There are numerous technical solutions in the prior art to separate already formed bubbles from circulation. Current perfusion practice generally targets mildly hyperoxic blood gases during CPB. This target is achieved by lowering the partial pressure of oxygen in oxygenator sweep gas by dilution with air, thereby engendering the needless side effect of dissolving nitrogen in blood. The blood, thus saturated with dissolved gas, is poorly able to dissolve gases that exist in bubble form as GME.
However, there is also a need to diminish the generation of gas bubbles, i.e. the formation of gas bubbles during heart surgery, for example. In a blood bubble, in the liquid-gas interface, there is an approximately 40-100 Å (i.e. 4-10 nanometer) deep layer of lipoproteins that denaturate due to direct contact with the foreign material, e.g. gas. In turn, the Hageman factor is activated which initiates coagulation and the concomitant adverse consumption of factors promoting coagulation, which in the post-pump period are desperately needed to prevent bleeding from the surgical wound.
Accordingly, a system and method capable of inhibiting the bubble formation in the blood in the absence of nitrogen during extracorporeal circulation would be desirable.